Arthroplasty process for securely anchoring prostheses to bone, and arthroplasty products therefor

ABSTRACT

A synovial prosthetic member includes a body having an articulating surface and an anchor surface, the articulating surface being configured for articulation with another articulating surface of a synovial joint, the anchor surface being configured for cementing to bone, the body being composed of ultrahigh molecular weight polyethylene (UHMWPE), the anchor surface having been subjected to treatment by either ion implantation, ion beam assisted deposition, or sputter deposition.

This application is a continuation of application Ser. No. 08/375,942filed on Jan. 20, 1995 now abandoned: Entitled "Arthroplasty Process forSecurely Anchoring Prostheses to Bone and Arthroplasty ProductsTherefor".

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to arthroplasty, i.e., an operation torestore motion between the bones of a skeletal joint, and concomitantfunction to muscles, ligaments and other tissue which control thatjoint. The present invention more particularly relates to cementingprostheses to bone.

2. The Prior Art

A prosthesis for a freely movable (synovial) skeletal joint comprises atleast one member that has a configuration which presents an articulatingsurface and an anchor surface. The anchor surface is anchored to bone.The articulating surface bears against the corresponding articulatingsurface of another member.

In conventional hip, knee and like arthroplasties, for example, a memberof a plastic or metal prosthesis is positioned with an anchor surfacethat is directly in contact with and mechanically anchored to boneeither with or without cement. In the absence of cement, the integrityof the anchor typically relies upon the configuration of the anchorsurface of the prosthesis member and intergrowth of bone and/or tissuewith that surface. In the presence of cement, the integrity of theanchor typically relies, not only on adhesion, but also upon mechanicalinterlocking between (1) the cured cement, and (2) the adjoining orconjunctive anchor surfaces of the prosthesis member and the bone.Various problems have been encountered in implementing the abovetechniques.

Metal prostheses conventionally have been composed of either a titaniumalloy or a cobalt-chromium alloy. Although these materials haveadvantages in strength and surface integrity, they may suffer fromproblems that include less than desired in vivo performance. Plasticprostheses conventionally have been composed of ultra high molecularweight polyethylene (UHMWPE), and the cement therefor conventionally hasbeen composed of polymethyl methacrylate (PMMA). These materials haveexcellent biocompatibility, but have suffered from poor adhesion to eachother, as a result of which loosening occurs and debris is produced.

SUMMARY OF THE INVENTION

The present invention is based on the discovery that the adhesionbetween a high molecular weight polyene and an alkyl polyacrylate cementis radically improved if the surface of the polyene, prior to cementing,is predeterminedly modified by ion implantation, ion beam assisteddeposition (IBAD), and/or sputter deposition.

The primary object of the present invention is to provide a prosthesisfor a synovial joint, characterized by at least one polymeric memberthat has, (1) for anchoring to bone, an anchor surface that has beenmodified by ion implantation, ion beam assisted deposition, and/orsputter deposition, and (2) an articulating surface that is adapted tobear against the corresponding articulating surface of another member ofthe prosthesis member. The object of the present invention morespecifically is to provide, in vivo, an assemblage comprising, incombination, such a prosthesis and a polymeric cement mantleinterconnecting the anchor surface of the prosthesis and contiguousbone. The polymeric member contains a polyethylene with a molecularweight of greater than 200,000 as one of its characteristic ingredients,preferably an ultrahigh molecular weight polyethylene with a molecularweight ranging from 3×10⁶ to 6×10⁶. The cement contains an acrylic resinbonding agent/cement as one of its characteristic ingredients,preferably polymethyl methacrylate.

Preferably, in the case of ion implantation, an infusion ofbiocompatible ions is concentrated primarily in the outer 25 μm of theanchor surface. Preferably in the case of ion beam assisted depositionand sputter deposition, a coating of deposited material ranges inthickness from 2 to 5,000 nm. It is believed that the mechanism forenhanced adhesion in the case of ion implantation is an increasedconcentration of carbonyl groups, hydroxyl groups and/or threedimensional cross links, by which the surface becomes more hydrophilic.It is believed that the mechanism for enhanced adhesion in the case ofIBAD and sputter deposition is the presence of inorganic atoms ormolecules at the anchoring interface and the superior adhesion of thecement to those inorganic atoms or molecules.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the presentinvention, reference is made to the following specification, which is tobe taken in connection with the accompanying drawings, wherein:

FIG. 1 is a flow diagram schematically illustrating a process of thepresent invention and a product thereof;

FIG. 2 schematically illustrates a ball and socket prosthesis adaptedfor shoulder arthroplasty in accordance with the present invention;

FIG. 3 schematically illustrates a hinge joint prosthesis adapted forfinger, elbow and knee arthroplasty in accordance with the presentinvention;

FIG. 4 schematically illustrates an ovoidal joint prosthesis adapted forwrist arthroplasty in accordance with the present invention;

FIG. 5 schematically illustrates a saddle joint prosthesis adapted forthumb joint arthroplasty in accordance with the present invention;

FIG. 6 schematically illustrates a pivot joint prosthesis adapted forforearm arthroplasty in accordance with the present invention;

FIG. 7 schematically illustrates a gliding joint prosthesis adapted forcarpus arthroplasty in accordance with the present invention;

FIG. 8 schematically illustrates a complete knee joint prosthesisadapted in accordance with the present invention;

FIG. 9 illustrates a bone cement adhesion test procedure for evaluatingtest results in accordance with the present invention;

FIG. 10 graphically illustrates bone cement adhesion shear strength testresults in accordance with the present invention;

FIG. 11 illustrates a micro-FTIR spectrum of a UHMWPE control sample inaccordance with the present invention;

FIG. 12 illustrates a micro-FTIR spectrum of nitrogen ion implantedUHMWPE in accordance with the present invention;

FIG. 13 shows nanohardness measurements of treated vs. untreated UHMWPE,illustrating certain principles of the present invention; and

FIG. 14 shows water contact angle measurements of treated vs. untreatedUHMWPE, illustrating certain principles of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The Flow Diagram of FIG. 1

FIG. 1 illustrates a pair of mating integral members 30, 32 of anartificial synovial joint. In the preferred embodiment, one member 30 iscomposed of metal or ceramic, and the other member 32 is composed of ahigh molecular weight polyene. Preferrably, in a spherical joint, suchas a hip joint, the metal or ceramic is a titanium alloy, acobalt-chromium alloy, an alumina ceramic, or a zirconia ceramic. Forall other joints, ceramic is not typically used and the metal is atitanium alloy or a cobalt-chromium alloy. Preferrably, the highmolecular weight polyene is an ultrahigh molecular weight polyethylene(UHMWPE). Members 30, 32 present contiguous articulating surfaces 34, 36and remote conjunctive anchor surfaces 38, 40. Articulating surfaces 34,36 have complementary configurations that constrain the members formovement under control of local muscles and with lubrication by synovialfluid.

As shown in FIG. 1, the present invention contemplates: modifying theanchor surface of the polymeric member 40 by ion implantation, ion beamassisted deposition (IBAD), or sputter deposition as at 44; matchingconfigurations 38, 40 of the anchor surfaces with complementary surfaces50, 52 of the bones 46, 48; interposing between the anchor surfaces andthe complementary surfaces 50, 52 an uncured cement as at 54, 56; and,while the cement is curing, to provide solid bonds 58, 60, compressingthe cement between each associated anchor surface 38, 40 andcomplementary surface 50, 52, and removing excess cement from thebone-prosthesis interfaces.

The metal member anchor surface 38 is shown as having a stem or ridge 62which projects into a corresponding medullary canal 64 or trough in thebone 46 to which it is to become affixed. The polymeric member anchorsurface 40 is shown as having a flat face 66 with protrusions 69, 71,and as being in close proximity with a corresponding flat face 68 of thebone 48 to which it is to become affixed, such that the ends of theprotrusions 69, 71 are in contact with the bone 48. Metallic screws 70,72 then connect member 32 to bone 48. The metallic screws 70, 72 mayextend from the member 32 to the bone 48 by passing through theprotrusions 69, 71, as in FIG. 1, or by bypassing the protrusions 69,71. Cement 54, 56 initially is composed of a methyl acrylatepolymerizate, and cures to cement mantles 58, 60 which are composed ofpolymethyl methacrylate (PMMA).

In an alternate embodiment, the metal member has a flat anchor face thatis in contiguity with the corresponding flat face of the bone to whichit is to become affixed, and the polymeric member has a stem or ridgewhich projects into a corresponding medullary canal or trough in thebone to which it is to become affixed.

In another alternate embodiment, both the metal member and the polymericmember have flat anchor faces that are in contiguity with thecorresponding flat faces of the bones to which they are to becomeaffixed.

In a further alternate embodiment, both the metal member and thepolymeric member have stems or ridges which project into correspondingmedullary canals or troughs in the bones to which they are to becomeaffixed.

Ion Implantation of the Anchor Surfaces

As indicated above and in FIG. 1, one process of the present inventioncontemplates treating the polymeric member anchor surface 40, prior tocementing, by ion implantation as at 44. An applicable ion implantationprocess is disclosed in U.S. Pat. No. 5,133,757, issued Jul. 28, 1992 inthe names of Piran Sioshansi and Richard W. Oliver, for "IonImplantation of Plastic Orthopaedic Implants." The specification of U.S.Pat. No. 5,133,757 is incorporated hereinto by reference.

Preferably, ion implantation of one or both conjunctive surfacesinvolves exposure by an ion beam to a dose in the range of 1×10¹³ to5×10¹⁷ ions/cm². Preferably, the ion beam is composed of gaseous orbiocompatible ions selected from the class consisting of argon (Ar),boron (B), carbon (C), gold (Au), hafnium (Hf), helium (He), hydrogen(H), iridium (Ir), niobium (Nb), nitrogen (N), oxygen (O), palladium(Pd), platinum (Pt), silicon (Si), silver (Ag), tantalum (Ta), titanium(Ti), and zirconium (Zr). The energy of such an ion beam preferablyranges from 5 to 1,000 keV (thousand electron volts).

In practice, hydrogen atoms implanted as above are concentrated at theanchor surface in a zone that is at most 25 μm deep, and the otherimplanted ions are concentrated at the anchor surface in a zone that isat most 2 μm deep. The ion implanted zone in either case containsconcentrations of carbonyl groups, hydroxyl groups and three-dimensionalcross-links that are at least 10% greater than those groups andcross-links in the main body of the member below the ion implanted zone.

Ion Beam Assisted Deposition on the Anchor Surfaces

Alternatively, as indicated above and in FIG. 1, another process of thepresent invention contemplates treating the polymeric member anchorsurface 40 by ion beam assisted deposition prior to cementing. Anapplicable ion beam assisted deposition process is disclosed in U.S.Pat. No. 5,236,509, issued Aug. 17, 1993 in the names of Piran Sioshansiand Raymond J. Bricault, Jr., for "Modular IBAD Apparatus for ContinuousCoating." The specification of U.S. Pat. No. 5,236,509 is incorporatedhereinto by reference.

Preferably, ion beam assisted deposition on one or both anchor surfacesinvolves simultaneous exposure in a vacuum to an ion source and anevaporation source, by which atoms from the evaporation source, in part,are driven into and onto the surface with assistance of the ion beam.The energy of the ion beam preferably is at least 50 eV (electronvolts), generating an ion fluence of about 1 ion per 1,000 atoms beingdeposited and with a current density of about 45 microamps per cm².

Preferably, the ion beam is selected from the class consisting ofhydrogen (H), helium (He), argon (Ar), nitrogen (N), and oxygen (O), andthe atoms and molecules from the evaporation source are selected fromthe class consisting of biocompatible elements such as carbon (C), gold(Au), palladium (Pd), platinum (Pt), silicon (Si), silver (Ag), tantalum(Ta), titanium (Ti), and zirconium (Zr), and oxide and nitride ceramicsof these elements. In practice, the resulting coating of such a depositon the anchor surface ranges in thickness from 2 to 5,000 nm.

Sputter Deposition on the Anchor Surfaces

Alternatively, as indicated above and in FIG. 1, another process of thepresent invention contemplates treating the polymeric member anchorsurface 40 by sputter deposition prior to cementing. Sputter depositionis a process by which a target material is bombarded by energeticparticles, causing some of the target material to be ejected from thetarget and deposited onto the surface of the substrate, the material tobe coated. Sputter deposition takes place in a vacuum, typically in therange of 1×10⁻³ to 5×10⁻⁷ Torr. The energetic particles are generallyions of a heavy inert gas, such as argon. In operation, the vacuumchamber in which the target and substrate are positioned is evacuatedand then backfilled with the inert gas to a pressure of from 1 to 100mTorr. The inert gas is subjected to an electrical charge, resulting inthe gas being ionized in the vicinity of the target. The target isnegatively charged, causing the positively charged ions to bombard itssurface.

One typical sputter deposition apparatus is called a diode system. Inthis apparatus, the same electrical source is used to ionize the inertgas and to negatively charge the target. In the diode system, theelectrical potential generally ranges from 200 to 5000 volts. When thetarget is an electrically conductive material, direct current can beused, and when the target is a non-electrically-conductive material, aradio frequency potential is applied to the target.

Preferably, the target material for sputter deposition is selected fromthe class consisting of biocompatible elements such as carbon (C), gold(Au), palladium (Pd), platinum (Pt), silicon (Si), silver (Ag), tantalum(Ta), titanium (Ti), and zirconium (Zr), and oxide and nitride ceramicsof the these elements. In practice, the resulting coating of such adeposit on the anchor surface ranges in thickness from 2 to 5,000 nm.

Preferably, a radio frequency diode sputter deposition system isemployed. The target is pure titanium and oxygen gas is mixed with theinert argon gas enabling the titanium and oxygen to combine to formtitanium dioxide (TiO₂). The sputtering chamber is backfilled with argonand oxygen gasses at a ratio of 3:1 to a pressure of 1 mTorr. Thedeposition rate is 0.3 nm/sec and the thickness of the depositedtitanium dioxide layer is 300 nm. The target voltage is 1000 V.

The Synovial Joints of FIGS. 2 to 8

The present invention is intended for application, in accordance withthe present invention, to a wide variety of well known prosthetic jointconfigurations, of which FIGS. 2 to 8 are examples. All of theillustrated prosthetic joints incorporate (1) a ultrahigh molecularweight polyethylene member, the anchor surface of which has been exposedto ion implantation, ion beam assisted deposition, or sputterdeposition, (2) a metal or ceramic member, and (3) polymethylmethacrylate mantles. FIG. 2 illustrates a hip or shoulder jointcomprising ball and socket articulating surfaces 74, 76, anchor surfaces78, 80, and cement mantles 82, 84, allowing angular movement in anydirection. FIG. 3 illustrates a joint for fingers, elbows, and knees,comprising hinged articulating surfaces 86, 88, anchor surfaces 90, 92,and cement mantles 94, 96, allowing angular movement only in one plane.FIG. 4 illustrates a joint for wrists, comprising ovoid articulatingsurfaces 98, 100, anchor surfaces 102, 104, and cement mantles 106, 108,the articulating surfaces being ovoidal so that only angular movement,but not rotation, of one bone in relation to the other is possible. FIG.5 illustrates a thumb joint comprising articulating saddle surfaces 110,112, anchor surfaces 114, 116, and cement mantles 118, 120, allowingmovement in two orthogonal directions. FIG. 6 illustrates a forearmjoint, comprising pivotal articulating surfaces 122, 124, anchorsurfaces 126, 128, and cement mantles 130, 132, such that one bonepivots about its own longitudinal axis. FIG. 7 illustrates a carpaljoint, comprising articulating glide surfaces 134, 136, anchor surfaces138, 140, and cement mantles 142, 144, characterized by two flatsurfaces that allow sliding in any planar direction.

FIG. 8 illustrates a more complicated joint configuration for knees thatincludes a femur-tibia joint and a femur-patella joint. Thisconfiguration includes a femoral member 160, a tibial member 162, and apatellar member 164. Preferrably, the femoral member 160 is metal andhas two articulating surfaces 166, 170 and one anchor surface 174 withcement mantle 180. Preferrably, the tibial member 162 is polymeric withone articulating surface 168 and one anchor surface 176 with cementmantle 182. Preferrably, the patellar member 164 is polymeric with onearticulating surface 172 and one anchor surface 178 with cement mantle184. The femur-tibia joint is a hinge joint similar to the hinge jointdescribed with reference to FIG. 3 and comprises articulating surfaces166, 168. The femur-patella joint is a sliding joint comprisingarticulating surfaces 170, 172, wherein the patellar member articulatingsurface 172 slides vertically within the femoral member articulatingsurface 170.

In an alternative embodiment, the two femoral articulating surfaces 166,170 are not discrete, but are contiguous.

EXAMPLE I UHMWPE

The characteristics of UHMWPE polymer are outstanding abrasionresistance; among the highest impact resistance of any plastic material;low coefficient of friction; nonstick, self-lubricating surface; goodchemical resistance; negligible water absorption; excellent energyabsorption and sound-dampening properties; and excellent dielectric andinsulating properties. This polymer does not melt, flow or liquify atits melting point of from 138 to 142° C. (280 to 289° F.), and retainsexcellent dimensional stability. Chemical resistance to aggressivemedia, including most strong oxidizing agents, is excellent. Exposure toaromatic and halogenated hydrocarbons results in only slight surfaceswelling if moderate temperature levels are maintained. The extremelyhigh processing viscosities characteristic of its high molecular weightrequire special processing procedures because the polymer resin does notexhibit a measurable melt index. The most common methods for fabricationof UHMWPE are ram extrusion and compression molding. In both cases,individual UHMWPE particles are fused into what appears to be a solid,although microscopically they remain as discrete particles withsegmented diffusion between them. Ram extrusion is accomplished bycontinuously feeding resin through a hopper into the extruder throat andthen packing the material at infrequent intervals with a reciprocatingplunger, thus removing the air phase. The compressed powder then movesthrough heated zones, where it is fused. The cross section of the barrelor die corresponds to the profile of the product. Production rates areinfluenced by the hydraulic system heater capacity, the die length, andthe strength of the construction materials. Typical extrusion rates are10 to 20 kg/h (22 to 44 lb/h). Controller set-point temperatures are 160to 230° C. (320 to 446° F.).

Material properties are listed in Table 1 below.

                  TABLE I                                                         ______________________________________                                        Property            Typical Values                                                                           Test Method                                    ______________________________________                                        Mechanical                                                                      Density, g/cm.sup.3 0.926-0.934 D 792                                         Tensile strength at yield, MPa (ksi) 21 D 638                                  (3.1)                                                                        Tensile strength at break, MPa (ksi) 48 D 638                                  (7.0)                                                                        Elongation at break, % 350 D 638                                              Young's modulus, GPa (10.sup.6 psi)                                           At 23° C. (73° F.) 0.69 D 638                                    (0.10)                                                                       At -269° C. (-450° F.) 2.97 D 638                                (0.43)                                                                       Izod impact strength, kJ/m (ft - lbf/in)                                      notch                                                                         At 23° C. (73° F.) 1.6 D 56(a)                                   (30)                                                                         At -40° C. (-40° F.) 1.1 D 56(a)                                 (21)                                                                         Hardness, Shore D 62-66 D 2240                                                Abrasion resistance 100 --                                                    Water absorption, % Nil D 570                                                 Relative solution viscosity, dl/g 2.3-3.5 D 4020                              Thermal                                                                       Crystalline melting range, 138-142 Polarizing                                 powder, ° C. (° F.) (280-289) microscope                        Coefficient of linear expansion,                                              10.sup.-4 4/K.                                                                At 20 to 100° C. (68 to 212° F.) 2 D 696                        At -200 to -100° C. (-330 to 0.5 D 696                                 -150° F.)                                                              Electrical                                                                    Volume resistivity, Ω - m >5 × 10.sup.14 D 257                    Dielectric strength, kV/cm (V/mil) 900 D 149                                   (2300)                                                                       Dielectric constant 2.30 D 150                                                Dissipation factor, × 10.sup.-4                                         At 50 Hz 1.9 D 150                                                            At 1 kHz 0.5                                                                  At 0.1 MHz 2.5                                                                Surface resistivity, wt % carbon                                              black, Ω                                                                At 0.2% for color >10.sup.14    D 257                                         At 2.5% for UV protection 10.sup.11 D 257                                     6.5% for antistatic applications 10.sup.5  D 257                              16.7% for conductive applica- 10.sup.3  D 257                                 tions                                                                       ______________________________________                                    

EXAMPLE II PMMA

The cement of the present invention is sold by Howmedica under the tradedesignation SURGICAL SIMPLEX P RADIOPAQUE BONE CEMENT. This productinitially is a mixture of polymethyl methacrylate monomer,methylmethacrylate styrene copolymer, and barium sulfate forradiopacity. Prior to use, the product is packaged in two sterilecomponents. One component is an ampule containing 20 ml of a colorless,flammable liquid monomer which has a sweet, slightly acrid odor, and isof the following composition:

    ______________________________________                                        Methyl methacrylate (monomer)                                                                        97.4% v/v                                                N,N-dimethyl-p-toluidine        2.6% v/v                                      Hydroquinone                    75 ± 15 ppm                                 -                                                                            Formula:                                                                                     ##STR1##                                                     ______________________________________                                    

Hydroquinone is added to prevent premature polymerization which mayoccur under certain conditions, e.g., exposure to light and elevatedtemperatures. N, N dimethyl-p-toluidine is added to promote cold curingof the finished therapeutic compound. The liquid component is sterilizedby membrane filtration.

The other component is a packet of 40 g of a finely divided whitepowder, a mixture of polymethyl methacrylate, methyl methacrylatestyrene copolymer, and barium sulfate, as follows:

    ______________________________________                                        Polymethyl methacrylate                                                                             15.0% w/w                                                 Methyl methacrylate styrene copolymer 75.0% w/w                               Barium sulfate 10.0% w/w                                                    ______________________________________                                         ##STR2##

The powder component is sterilized by gamma irradiation.

At the time of use, the powder and liquid are mixed, resulting in theexothermic polymeric formation of a soft, pliable, dough-like mass.Within a few minutes, as the reaction progresses, a hard, cement-likecomplex is formed. Upon completion of polymerization, the cement servesas a buffer for even weight distribution and other stresses between theprosthesis and bone. After application and during the completion of thepolymerization process of the cement in situ, positioning of theprostheses is maintained securely without movement to obtain properfixation. The completion of polymerization occurs in the patient and isan exothermic reaction with considerable liberation of heat.Temperatures occurring during the polymerization have been reported ashigh as 110° C.

EXAMPLE III Test Procedures

The test procedure illustrated in FIG. 9 demonstrates the advantages ofthe present invention as follows: Ten treated (test samples) and fiveuntreated (control samples) UHMWPE cylinders, of the type shown at 146,are bonded axially within aluminum rings of the type shown at 148, byPMMA bone cement of the type shown at 150. The treated test samples aresubjected to ion implantation, ion beam assisted deposition, or sputterdeposition as discussed above. In the case of the ion implantation testsamples, the anchor surfaces are exposed to a nitrogen ion beam to adose of approximately 1×10¹⁶ ions/cm² at an energy level of 140 keV. Inthe case of the IBAD test samples, titanium is deposited to a thicknessof approximately 300 nm. In the case of the sputter deposition testsamples, titanium dioxide is deposited to a thickness of approximately300 nm. Shear tests of the cylinder-cement interfaces are performed bypulling the cylinders axially with respect to the rings. The forcesnecessary to remove the cylinders from the rings are depicted in FIG.10, which shows that the adhesion shear strength is an order ofmagnitude greater for the treated cylinders than for the untreatedcylinders. FIG. 11 illustrates a micro-FTIR spectrum a control sampleand FIG. 12 illustrates a micro-FTIR spectrum of a test sample implantedwith nitrogen. A comparison of these spectra indicates a high level ofO--H (hydroxyl), C═O (carbonyl), and C--H (cross-linking) groups at thesurfaces of the test samples relative to the surfaces of the controlsamples. FIG. 13 shows how much greater the nanohardness of the testssamples is relative to the control samples. FIG. 14 shows that the watercontact angle of the test samples is lower relative to the controlsamples and, therefore, that the surfaces of the test samples are morehydrophilic than the surfaces of the control samples.

Operation

In operation, first the anchor surface of a prosthesis member is infusedby ion implantation, coated by ion beam assisted deposition, or coatedby sputter deposition. Next, the anchor surface is fitted to acomplementary surface of bone, in the presence of a mixture of monomericmethyl methacrylate and a curing agent. Then curing occurs. The resultis a synovial prosthetic member comprising a body having an articulatingsurface and an anchor surface, and a cement mantle by which the anchorsurface is bonded to bone. This member thereby becomes a component of asynovial joint that is characterized by mated articulating surfaces.

What is claimed is:
 1. A method for preparing a prosthetic implant whichincludes a bone-engaging surface having enhanced adhesioncharacteristics for cement, comprising the steps of:disposing aprosthetic implant having a bone-engaging surface and an articulatingsurface in an ion treatment chamber; and subjecting the bone-engagingsurface of said prosthetic implant to ion beam treatment, such that saidion treated bone-engaging surface of said prosthetic implant hasenhanced adhesion characteristics for cement.
 2. The method of claim 1,wherein said prosthetic implant is composed of a metal.
 3. The method ofclaim 2, wherein said metal is a titanium alloy or a cobalt-chromiumalloy.
 4. The method of claim 1, wherein said prosthetic implant iscomposed of a ceramic.
 5. The method of claim 4, wherein said ceramic isan alumina ceramic or a zirconia ceramic.
 6. The method of claim 1,wherein said prosthetic implant is composed of a polymer.
 7. The methodof claim 6, wherein said polymer is a high molecular weight polyene. 8.The method of claim 7, wherein said high molecular weight polyene is anultrahigh molecular weight polyethylene (UHMWPE).
 9. The method of claim8, wherein said UHMWPE has a molecular weight of greater than 200,000.10. The method of claim 8, wherein said UHMWPE has a molecular weight ofbetween about 3×10⁶ to about 6×10⁶.
 11. The method of claim 1, whereinsaid surface is treated with at least one species of atoms selected fromthe group consisting of argon (Ar), boron (B), carbon (C), gold (Au),hafnium (Hf), helium (He), hydrogen (H), iridium (Ir), niobium (Nb),nitrogen (N), oxygen (O), palladium (Pd), platinum (Pt), silicon (Si),silver (Ag), tantalum (Ta), titanium (Ti), and zirconium (Zr).
 12. Themethod of claim 1, wherein said surface treatment of said bone-engagingsurface results in a surface which is coated with ions, embedded withions, or is coated and embedded with ions.
 13. The method of claim 12,wherein said surface has a coating of ions from 2-5000 nm.
 14. Themethod of claim 12, wherein said surface has ions embedded between about2 and 25 μm deep.